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Oil from the Deepwater Horizon oil spill is seen at sunset off East Grand Terre Island, where the Gulf of Mexico meets Barataria Bay, on the Louisiana coast on July 31. Top left is Grand Isle. ((Gerald Herbert/Associated Press))

Engineers will start shoving mud and maybe cement into the blown-out oil well in the Gulf of Mexico on Tuesday in what could be one of the final steps to plug it for good, BP said Monday.

BP senior vice-president Kent Wells said that crews will likely start the "static kill" attempt Tuesday if tests Monday determine the well can withstand the mud.

There's no guarantee of success, and BP engineers still plan to follow up the static kill days later by sending a stream of mud and cement into the bottom of the 1.6-kilometre-deep underground reservoir through a relief well they've been digging for months.

But the oil giant's engineers and petroleum experts say it's the clearest path yet to choke the blown-out well and make it even easier for the crews drilling the relief well to ensure oil can never again erupt from the deep-sea well, which has spewed as much as 697 million litres since the rig connected to it blew up in April and killed 11 workers.

The only thing keeping millions more gallons of oil out of the Gulf right now is an experimental cap that has held for more than two weeks but was never meant to be permanent.

The developments have the makings for an interesting week.

"It could be the beginning of the end," said Darryl Bourgoyne, director of Petroleum Engineering Research Lab at Louisiana State University.

Pumping mud

When the static kill begins, crews will slowly pump heavy mud through lines installed last month straight down the throat of the leaky well. If the mud forces the oil back into the massive underground reservoir and scientists are confident the pressure remains stable, then engineers can pump in fresh cement to seal it.

"The only thing that separates the oil from the sea now is the valve. This puts thousands of feet of mud and cement in between," said Eric Smith, associate director of the Tulane Energy Institute.

"The idea is to have as many barriers as possible between the ocean and the reservoir. We're adding an extra level of safety."

Officials may then begin the process of choking the underground reservoir feeding the well by pumping mud and then cement down an 5,500-metre relief well.

BP officials have long said the process is the only sure way to choke the well for good — plugging up the source of the oil, not just its route to the sea.

If the static kill attempt sounds familiar, that's because it is. The company tried a similar process, called a top kill, to choke the well with mud in May. It failed partly because the mud couldn't overcome the flow of the oil.

There's reason to hope this time will be different. For one, the oil is no longer freely flowing from the well, thanks to the temporary cap. That means that engineers won't have to pump in mud with as much force, Wells said.

There's always the risk that the pressure exerted by the mud will rupture the casing holding in the oil and potentially cause an even greater mess, but experts say it's very unlikely.

"I can't imagine it failing. It's holding pressure and there's no indication of any loss of fluid from the well," Smith said. "It's a vanishingly small risk of failure."

Late August completion

The whole procedure is still set to be completed by late August despite a brief evacuation for tropical storm Bonnie last week. Federal officials are also downplaying its importance in case of a failure. Retired coast guard Admiral Thad Allen, the government's point man on the recovery effort, said Sunday that "static kill is not the end all, be all."

BP has had more than its share of failures experimenting with other ambitious efforts. So if the oil is already contained and the completion of the relief well appears to be just around the corner, why is the oil giant even bothering to attempt the complicated static kill?

One answer is that it should make it easier to finish the relief well. Crews are also drilling a second, backup relief well.

If the static kill is successful, though, Smith said they likely wouldn't have to use as much mud to choke the oil. It's also a good way for BP to hedge its bets in case the relief well takes longer than expected to work, he said.

There's a third reason the company has embraced the static kill. Each day the temperature of Gulf of Mexico waters increases, so does the threat of another violent storm disrupting the cleanup process. Federal officials are hoping to end the oil threat once and for all before peak hurricane season, which typically lasts from mid-August to late October.

"If we can get this thing shut in permanently before the August hurricane season, we will have dodged a huge bullet," said Rear Admiral Paul Zukunft, the government's on-scene co-ordinator.